1. Field of the Invention
The invention relates to a vehicle suspension system employed in a motor vehicle, such as a four-wheel vehicle, and in particular to a vehicle suspension system that includes vehicle behavior controllers that control the motion of each suspension device (e.g., hydraulic cylinder for suspension) mounted with respect to each of all right and left wheels, and is adapted to control or suppress particular types of behavior, such as bouncing, pitching and rolling, of a vehicle body.
2. Description of Related Art
An example of a vehicle suspension system of the above type is disclosed in, for example, Japanese laid-open Patent Publication No. 6-509997. In the vehicle suspension system disclosed in this publication, suspension hydraulic cylinders respectively mounted with respect to front and rear, right and left wheels of the vehicle are diagonally connected to each other by hydraulic pipes, so that the suspension system can suppress pitching and rolling of the vehicle body while assuring sufficient road-holding characteristic of the wheels on an unleveled ground.
The operating characteristics of the vehicle suspension system as shown in the above-indicated publication are determined by accumulators (e.g., gas springs) connected to and communicating with respective hydraulic pipes for connecting diagonally located cylinders, or accumulators connected to and communicating with the hydraulic pipes for connecting diagonally located cylinders and a single load distribution unit, or an actuator that includes a single load distribution unit to which the hydraulic pipes for connecting diagonally located cylinders are connected for fluid communication. With this arrangement, the operating characteristics of the suspension system cannot be individually or separately set for suppressing each type of vehicle behaviors, such as pitching and rolling, of the vehicle body. Thus, it has been difficult to set the operating characteristics of the suspension system suitable for each type of vehicle behavior.
In addition, the known vehicle suspension system as described above is constructed such that a pair of hydraulic chambers formed on the opposite sides of a piston in each of the suspension hydraulic cylinders are diagonally connected to a pair of hydraulic chambers formed in a corresponding suspension hydraulic cylinder that is located in a diagonal relationship with the above-indicated hydraulic cylinder. Namely, two ports formed in each of the suspension hydraulic cylinders are diagonally connected to two ports formed in the corresponding suspension hydraulic cylinder, to thus provide two hydraulic pipe systems. Thus, the hydraulic pipes are arranged in a complicated manner, which results in increased cost and weight of the pipes, and eventually those of the suspension system. While the vehicle suspension system as described above is able to suppress pitching and rolling of the vehicle body, the system is not able to suppress bouncing (i.e., behavior in the heaving direction) of the vehicle body.